In order to provide a joint replacement in the human body, it is necessary to prepare the bone and/or implant such that a proper fit is achieved. Further, the implant must fulfil the requirements of bio-functionality and, therefore, must be accurately arranged and orientated.
Prior to the availability of image-assisted or navigation-assisted surgery, the only way to orientate an implant was to predefine its modification by producing five planes with the aid of different positioning instruments such as, for example, an intramedullary pin. This technique is illustrated in FIG. 2, which shows a bone 1′ that has been ablated on a sequence of five planes 3′. An implant 2′ provided with a inner contour corresponding to the ablated bone 1′ is shown placed onto the bone 1′.
The above method is very invasive, e.g., a great deal of bone material is ablated. Moreover, the orientation of the implant often is not very accurate.
Nowadays, navigated cutting blocks are used such that predefined areas on the bone can be ablated or produced. This improves the orientation of the implant, but smooth cuts still require significant bone removal.